Method and system for call setup

ABSTRACT

Aspects of the disclosure provide a method for setting up a call for a user equipment. The method includes receiving, by the user equipment, a measurement configuration message that specifies a set of measurement events corresponding to poor signal quality between the user equipment and a packet-switched network, and sending, by the user equipment, a measurement report when one of the set of measurement events occurs while performing a first call setup process for setting up the call using the packet-switched network. The method also includes terminating the first call setup process after sending the measurement report that indicates poor signal quality between the user equipment and the packet-switched network, and sending, by the user equipment, a service request to begin a second call setup process for setting up the call for the user equipment using a circuit-switched network after terminating the first call setup process.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.15/355,429, filed Nov. 18, 2016 which claims the benefit of U.S.Provisional Application No. 62/257,758, “Signal based alerting CSFB orpre-alerting CSFB during IMS call setup (eVoLTE)” filed on Nov. 20,2015. The contents of the above-noted applications are incorporatedherein by reference in their entirety.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Many communication standards have been developed to meet the demands formobile communications. Example communication standards include GlobalSystem for Mobile communications (GSM), General Packet Radio Service(GPRS) technology, Enhanced Data rates for Global Evolution (EDGE)technology, Universal Mobile Telecommunications System (UMTS), WorldwideInteroperability for Microwave Access (WiMAX) technology, and Long TermEvolution (LTE) technology, and the like. When setting up a voice callfor a mobile terminal (or sometimes also referred to as a user equipmentor UE), some communication standards rely upon circuit-switchednetworks, and some communication standards rely upon packet-switchednetworks. A service provider may implement a service network that offerssetting up a voice call for a mobile terminal using either acircuit-switched network or a packet-switched network. While setting upa voice call, the service network may first attempt to use thepacket-switched network, and may use the circuit-switched networkinstead when the signal quality between the mobile terminal and thepacket-switched network is poor. In some applications according to theLTE standards, changing from the packet-switched network to thecircuit-switched network when setting up a call is also known as theCircuit Switched Fallback (CSFB) functionality in the 3rd GenerationPartnership Project Technical Specification (3GPP TS) 23.272.

SUMMARY

Aspects of the disclosure provide a method for setting up a call for auser equipment. The method includes receiving, by the user equipment, ameasurement configuration message that specifies a set of measurementevents corresponding to poor signal quality between the user equipmentand a packet-switched network, and sending, by the user equipment, ameasurement report when one of the set of measurement events occurswhile performing a first call setup process for setting up the callusing the packet-switched network. The method also includes terminatingthe first call setup process after sending the measurement report thatindicates poor signal quality between the user equipment and thepacket-switched network, and sending, by the user equipment, a servicerequest to begin a second call setup process for setting up the call forthe user equipment using a circuit-switched network after terminatingthe first call setup process.

In an embodiment, the set of measurement events may include a firstevent where a signal strength from a base station that communicativelyconnects the user equipment and the packet-switched network becomes lessthan a first threshold, a second event where a signal strength from aneighboring base station becomes better than a second threshold, or athird event that is a combination of at least the first event and thesecond event.

The method may further include initiating the first call setup processby the user equipment, receiving a termination message after sending themeasurement report, and sending the service request in response toreceiving the termination message. The termination message may indicatetermination of the first call setup process without requesting the userequipment to perform retry attempts.

In an embodiment, the method may further include initiating the firstcall setup process by the user equipment, starting a timeout timer whensending the measurement report, and sending the service request afterthe timeout timer reaches a predetermined value.

The method can also include initiating the first call setup process bythe user equipment, starting a timeout timer when sending themeasurement report, and receiving a termination message after sendingthe measurement report. The method may include sending the servicerequest in response to an earlier one of receiving the terminationmessage and the timeout timer reaching a predetermined value.

Also, the method may further include receiving, by the user equipment,an invite message that indicates initiation of the first call setupprocess, receiving a cancellation message after sending the measurementreport, and receiving a service notification message after receiving thecancellation message. The method may include sending the service requestin response to receiving the service notification message. Thecancellation message may indicate termination of the first call setupprocess, and the service notification message may indicate initiation ofthe second call setup process.

In some embodiments, the method also includes sending, by a base stationthat communicatively connects the user equipment and the packet-switchednetwork, the measurement configuration message to the user equipment,receiving, by the base station, the measurement report from the userequipment, and determining whether to terminate the first call setupprocess and to begin the second call setup process based on at least themeasurement report from the user equipment.

Additionally, the method may include receiving, by the base station, acreate bearer request from an Internet Protocol Multimedia Subsystem(IMS), and sending, by the base station to the IMS in response to thecreate bearer request, a create bearer response that indicates adetermination result of whether to terminate the first call setupprocess and to begin the second call setup process.

Aspects of the disclosure further provide a user equipment that includesa transceiver and a controller. The transceiver may be configured tocommunicate with a packet-switched network and a circuit-switchednetwork. The controller may be configured to receive, through thetransceiver, a measurement configuration message that specifies a set ofmeasurement events corresponding to poor signal quality between the userequipment and a packet-switched network, send, through the transceiver,a measurement report when one of the set of measurement events occurswhile performing a first call setup process for setting up a call forthe user equipment using the packet-switched network, terminate thefirst call setup process after sending the measurement report thatindicates poor signal quality between the user equipment and thepacket-switched network, and send, through the transceiver, a servicerequest to begin a second call setup process for setting up the call forthe user equipment using the circuit-switched network after terminatingthe first call setup process.

In an embodiment, the set of measurement events may include a firstevent where a signal strength from a base station that communicativelyconnects the user equipment and the packet-switched network becomes lessthan a first threshold, a second event where a signal strength from aneighboring base station becomes better than a second threshold, or athird event that is a combination of at least the first event and thesecond event.

Also, the user equipment may be configured to initiate the first callsetup process or receive an invite message that indicates initiation ofthe first call setup process.

Aspects of the disclosure further provide a communication system thatincludes a service network and a user equipment configured tocommunicate with the service network. The service network may send ameasurement configuration message that specifies a set of measurementevents corresponding to poor signal quality between the user equipmentand a packet-switched network of the service network. The user equipmentmay receive the measurement configuration message, send a measurementreport when one of the set of measurement events occurs while performingthe first call set-up process, terminate the first call setup processafter sending the measurement report that indicates poor signal qualitybetween the user equipment and the packet-switched network, and send aservice request to begin a second call setup process for setting up thecall for the user equipment using a circuit-switched network afterterminating the first call setup process.

In an embodiment, the service network may include an Internet ProtocolMultimedia Subsystem (IMS) and a base station. The base station canreceive a create bearer request from the IMS, and send a create bearerresponse that indicates a determination result of whether to terminatethe first call setup process and to begin the second call setup processto the IMS in response to the create bearer request.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of this disclosure that are proposed as exampleswill be described in detail with reference to the following figures,wherein like numerals reference like elements, and wherein:

FIG. 1 shows an exemplary block diagram of a communication system forillustrating setting up a call for a user equipment, including changingfrom using a packet-switched network to a circuit-switched network,according to an embodiment of the disclosure;

FIG. 2 shows an exemplary signaling diagram of setting up an outgoingcall for the user equipment in the communication system in FIG. 1according to an embodiment of the disclosure;

FIG. 3 shows an exemplary signaling diagram of setting up an incomingcall for the user equipment in the communication system in FIG. 1according to an embodiment of the disclosure; and

FIG. 4 shows a flow chart outlining an exemplary process for changingfrom performing a first call setup process to a second call setupprocess in order to setup a voice call for a user equipment, such as theuser equipment in FIG. 1, according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

A person having ordinary skill in the art would appreciate that variouscomponents and communication interfaces described in the presentdisclosure are well known in the pertinent technology fields, asprovided in the corresponding 3GPP technical specifications thatcorresponds to the GSM, EDGE, GPRS, UMTS, and/or LTE standards. However,it should be understood that the disclosed embodiments are not limitedto the applications in the context of the GSM, EDGE, GPRS, UMTS, and/orLTE standards as defined by the 3GPP.

In some applications, the CSFB functionality may be implemented by LTESingle Radio Voice Call Continuity (SRVCC) if the service provider hasconfigured the service network to support such features. In accordancewith the present disclosure, the CSFB functionality may be implementedby using signaling messages, requests, or responses that have beenimplemented in the service network even when the service network is notconfigured to offer the SRVCC feature.

FIG. 1 shows an exemplary block diagram of a communication system 100for illustrating setting up a call for a user equipment (UE) 110,including changing from using a packet-switched network to acircuit-switched network, such as from a Evolved Packet Core (EPC)network 120 to a Circuit Switched (CS) core network 130, according to anembodiment of the disclosure.

The communication system 100 includes the UE 110, the EPC network 120,the CS core network 130, a package core network 140, an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) 126, a GSM EDGERadio Access Network (GERAN) 136, and a Universal Terrestrial RadioAccess Network (UTRAN) 146. The communication system 100 may furtherinclude a public switched telephone network (PSTN) 150, a packet datanetwork (PDN) 160, and an IP multimedia subsystem (IMS) 170. Theconfigurations and communication interfaces as depicted in FIG. 1 may becompatible with the GSM, EDGE, GPRS, UMTS, and/or LTE standards asdefined by the 3GPP.

The EPC network 120 may, for example, be implemented based on the LTEstandard and may include a Mobility Management Entity (MME) 122 as amain controller thereof. The EPC network 120 can communicate with theE-UTRAN 126 using an S1 interface and with the PDN 160 using at least anSGi interface. The E-UTRAN 126 may be implemented based on the LTEstandard and may include an Evolved Node B (eNB) 128 that can functionas a base station and communicate with the UE 110 using a LTE-Uuinterface.

The CS core network 130 may be implemented based on the GSM/EDGE/GPRSstandards and may include a Mobile Switching Center (MSC) 132 as a maincontroller thereof. The CS core network 130 can communicate with theGERAN 136 using an A interface, with the UTRAN 146 using an IuCSInterface, and with the PSTN 150 through dedicated signal paths 152. TheGERAN 136 may be implemented based on the GSM/EDGE/GPRS standards andmay include a Base Transceiver Station (BTS) 138 that can function as abase station and communicate with the UE 110 using an Um interface.

The packet core network 140 may be implemented based on the GPRS and/orUMTS standards and may include a Serving GPRS Support Node (SGSN) 142 asa main controller thereof. The packet core network 140 can communicatewith the UTRAN 146 using an IuPS interface, with the GERAN 136 using aGb interface, and with the PDN 160 using a Gi interface. The UTRAN 146may be implemented based on the UMTS standard and may include a Node B(NB) 148 that can function as a base station and communicate with the UE110 using a Uu interface. The EPC 120 and the packet core 140 maycommunicate with each other using at least an S3 interface. The EPC 120and the CS core network 130 may communicate with each other using atleast an SGs interface.

Further, the IMS 170 can be implemented based on the LTE standard andcommunicatively coupled with the PDN 160 and the PSTN 150. The IMS 170may include a Call Session Control Function (CSCF) controller 172 and aService Centralization and Continuity Application Server (SCC AS) 174.The MME 122 of the EPC 120 and the SGSN 142 of the packet core network(140) can be communicatively coupled with the IMS 170 via the PDN 160.

In the present disclosure, the combination of one or more of the EPC120, E-UTRAN 126, CS Core network 130, GERAN 136, Packet Core network140, UTRAN 146, PSTN 150, PDN 160, and IMS 170 may also be referred toas a service network.

In operation, the eNB 128 may send to the UE 110 a measurementconfiguration message that specifies a set of measurement eventscorresponding to poor signal quality between the UE 110 and apacket-switched network, such as the EPC 120, and particularly betweenthe UE 110 and the eNB 128 that connects the UE 110 with the EPC 120.While performing a call setup process for setting up a call for the UE110 using the EPC 120, the UE 110 may monitor the signal quality andsend a measurement report to the eNB 128 when one of the set ofmeasurement events as specified in the measurement configuration messageoccurs. The eNB 128 may determine, based on at least the measurementreport from the UE 110, whether to terminate the call setup process forsetting up the call using the EPC 120 and to initiate another call setupprocess for setting up the call using the circuit-switched network, suchas the CS Core network 130 EPC. The eNB 128 may receive a create bearerrequest from the CSCF controller 172 of the IMS 170 and send in responseto the create bearer request a create bearer response that indicates adetermination result of whether to terminate the first call setupprocess and to begin the second call setup process to the CSCFcontroller 172. The UE 110 may terminate the call setup process thatuses the EPC 120 after sending the measurement report and then send aservice request to the MSC 132 of the CS Core network 130 to beginanother call setup process for setting up the call using the CS Corenetwork 130.

In some examples, in addition to the measurement report from the UE 110,the eNB 128 may further consider whether the current call setup processhas been completed successfully, the current status of the call setupprocess, whether a Session Initiation Protocol (SIP) 180 RingingResponse has been received, or whether the service network supports theSRVCC feature, and the like. Also, the create bearer request and thecreate bearer response may be an LTE Create Bearer Request and an LTECreate Bearer Response as defined in the LTE standards.

The eNB 128 may send the measurement configuration message before orduring the call setup process for setting up a call for the UE 110 usingthe EPC 120. The set of measurement events may include a first eventwhere a signal strength from a base station that connects the UE 110 andthe EPC 120 becomes less than a first threshold, a second event where asignal strength from a neighboring base station becomes better than asecond threshold, and/or a third event that is a combination of at leastthe first event and the second event. In some examples, the set ofmeasurement events may include the LTE A1, B1, and/or B2 measurementevents. Also, the measurement configuration message may be implementedusing a LTE radio resource control (RRC) connection reconfigurationmessage.

In one example, the UE 110 is an originating terminal that makes anoutgoing voice call. The UE 110 initiates a first call setup processthat attempts to set up a voice call for the UE 110 using the EPC 120 bysending a request to the CSCF controller 172 and the SCC AS 174 of theIMS 170. The request for initiating the call may be an SIP INVITERequest. The UE 110 may receive the measurement configuration messagefrom the eNB 128 before or after the initiation of the first call setupprocess. While performing the first call setup process, when one of theset of measurement events specified by the measurement configurationmessage occurs, the UE 110 may send a measurement report that reportsthe occurrence of such measurement event, which indicates that thesignal quality between the UE 110 and the eNB 128 may not be good enoughfor successfully setting up a call using the EPC 120.

After sending the measurement report, the UE 110 may wait for atermination message from the CSCF controller 172 of the IMS 170 thatinforms termination of the first call setup process. The UE 110 then maysend the service request to initiate the second call setup process forsetting up the voice call for the UE 110 using the CS core network 130in response to receiving the termination message. In some example, thetermination message indicates termination of the first call setupprocess without requesting the UE 110 to perform retry attempts. Thetermination message may be an SIP 500 Server Internal Error response oran SIP 503 Service Unavailable response without requesting the UE 110 tomake any retry attempts. Also, the service request may be an LTEExtended Service Request.

Additionally or alternatively, the UE 110 may start a timeout timer whensending the measurement report. The UE 110 may send the service requestto initiate the second call setup process for setting up the voice callfor the UE 110 using the CS core network 130 after the timeout timerreaches a predetermined value. The UE 110 may optionally send acancellation message to the CSCF controller 172 of the IMS 170 when thetimeout timer reaches the predetermined value. In some example, if theUE 110 receives the termination message from the CSCF controller 172 ofthe IMS 170 before the timeout timer reaches the predetermined value,the UE 110 may also send the service request to initiate the second callsetup process in response to receiving the termination message beforethe timeout timer reaches the predetermined value.

The predetermined value for the timeout timer may range from fiveseconds to ten seconds. In some examples, the predetermined value forthe timeout timer may be set based on network operator's silent redialprotection period. In at least one example, the predetermined value forthe timeout timer may be set to be equal to or less than the networkoperator's silent redial protection period. Moreover, the cancellationmessage send by the UE 110 to the CSCF controller 172 of the IMS 170 maybe an SIP CANCEL Request.

In another example, the UE 110 is a terminating terminal that receivesan incoming voice call. The UE imitates a first call setup process thatattempts to set up a voice call for the UE 110 using the EPC 120 inresponse to a request from the CSCF controller 172 and the SCC AS 174 ofthe IMS 170. The request for initiating the call may also be an SIPINVITE Request. Similar to initiating an outgoing voice call, the UE 110may receive the measurement configuration message from the eNB 128before or after the initiation of the first call setup process forsetting up the incoming voice call. While performing the first callsetup process, when one of the set of measurement events specified bythe measurement configuration message occurs, the UE 110 sends ameasurement report that reports the occurrence of such measurementevent, which indicates that the signal quality between the UE 110 andthe eNB 128 may not be good enough for successfully setting up a callusing the EPC 120.

After sending the measurement report, the UE 110 may wait for acancellation message from the CSCF controller 172 of the IMS 170 thatinforms cancellation of the first call setup process. After receivingthe cancellation message, the UE 110 may receive a service notificationmessage from the EPC 120 that indicates initiation of a second callsetup process for setting up the voice call using the CS core network130. The UE 110 then may send a service request to initiate the secondcall setup process for setting up the voice call for the UE 110 usingthe CS core network 130 in response to receiving the servicenotification message. In some example, the cancellation message may bean SIP CANCEL Request. Also, the service request may be an LTE ExtendedService Request.

The UE 110 includes a transceiver 112 and a call setup controller 114.The transceiver 112 may be configured to communicate with apacket-switched network and/or a circuit-switched network, such as theeNB 128 according to the LTE standards, the NB 148 according to the UMTSstandards, and/or the BTS 138 according to the GSM/EDGE/GPRS standards.The call setup controller 114 is configured to perform the first andsecond call setup processes and manage the changing from performing thefirst to the second call setup processes as described in the presentdisclosure.

The UE 110 may also include a processor 116 and a memory 118. The memory118 may store program instructions, and the processor 116 can executethe program instructions stored in the memory 118 in order to performvarious predetermined functions. The processor 116 can include a singleor multiple processing cores. Various components of the transceiver 112and/or the call setup controller 114 may be implemented by hardwarecomponents, the processor 116 executing the program instructions, or acombination thereof. Of course, the processor 116 can also executeprogram instructions to control other operations of the UE 110 that arenot discussed in this disclosure.

The memory 118 can be used to store the program instructions,information corresponding to the set of measurement events, measurementresults, base stations such as BTS 138, NB 148, and/or eNB 128, and/orintermediate data. In some examples, the memory 118 includes anon-transitory computer readable medium, such as a semiconductor orsolid-state memory, a random access memory (RAM), a read-only memory(ROM), a hard disk, an optical disk, or other suitable storage medium.In some embodiments, the memory 118 includes a combination of two ormore of the non-transitory computer readable mediums listed above.

FIG. 2 shows an exemplary signaling diagram of setting up an outgoingcall for a user equipment (UE) 210 in a communication system, such asthe UE 110 in the communication system 100 in FIG. 1, according to anembodiment of the disclosure. FIG. 2 shows a signaling sequence amongvarious components, including the UE 210, eNB 228 of an E-UTRAN, MME 222of an EPC, CSCF controller 272 and SCC AS 274 of an IMS, and MSC 232 ofa CS Core network, which may correspond to the UE 110, eNB 128, MME 122,CSCF controller 172, SCC AS 174, and MSC 132 in FIG. 1, respectively.FIG. 2 only highlights example components and messages for illustratingthe disclosed embodiments. It is understood that additional messages,requests, or responses may be exchanged among the components depicted inFIG. 2, and additional components of the communication network may alsobe used for performing the signaling sequence depicted in FIG. 2.

At S210, the eNB 228 sends to the UE 210 a measurement configurationmessage that specifies a set of measurement events corresponding to poorsignal quality between the UE 210 and the packet-switched network,particularly the poor quality between the UE 210 and the eNB 228 thatconnects the UE 210 to the EPC. The set of measurement events mayinclude the LTE A1, B1, and/or B2 measurement events. Also, themeasurement configuration message may be implemented using a LTE RadioResource Control (RRC) connection reconfiguration message.

At S222, the UE 210 sends a request for initiating a voice call to theCSCF controller 272, such as an SIP INVITE Request. At S224, the CSCFcontroller 272 forwards the request for initiating the voice call to theSCC AS 274. At S226, the SCC AS 274 sends to the CSCF controller 272 aresponse indicating that the requested call setup process is inprogress, such as an SIP 183 Session in Progress Response. At S228, theCSCF controller 272 may further pass the response indicating that thecall setup process is in progress to the UE 210.

Although S210 as depicted in FIG. 2 is performed prior to S222, in someexamples, S210 may be performed after S222 or after S228. In someexamples, S210 may not be performed after the requested voice call issuccessfully setup using the packet-switched network.

At S232, when the UE 210 determines that one of the measurement eventsas specified in the measurement configuration message occurs, the UE 210sends a measurement report to the eNB 228. Also, at S234, the UE 210 maystart a timeout timer when sending the measurement report. Apredetermined timeout value for the timeout timer may range from fiveseconds to ten seconds. In some examples, the predetermined value forthe timeout timer may be set based on network operator's silent redialprotection period. In at least one example, the predetermined value forthe timeout timer may be set to be equal to or less than the networkoperator's silent redial protection period.

At S242, the CSCF controller 272 may send a request to create a bearerfor the voice call. S242 may include the CSCF controller 272 asking aPolicy and Charging Rules Function (PCRF) controller to send a sessionmodification message to a Packet Data Network Gateway (P-GW) of the EPC,and the P-GW may pass the request to the MME 222 using an LTE CreateBearer Request. The MME 222 may further send an LTE Bearer Setup Requestto the eNB 228. At S244, in response to the LTE Bearer Setup Request,the eNB 228 determines whether to abort the voice call setup processbased on the measurement report from the UE 210, the status of the callsetup process, or whether the service network support the SRVCC feature,or the like. When the eNB 228 determines to terminate the call setupprocess for setting up the voice call using the EPC and to initiateanother call setup process for setting up the voice call using the CSCore network, at S246 the eNB 228 informs the CSCF controller 272 thedecision in a response to the request to create a bearer. S246 mayinclude the eNB 228 sending the determination result to the MME 222using an LTE Bearer Setup Response. The MME 222 may forward thedetermination results to the P-GW using a LTE Create Bearer Response,and P-GW may forward the determination result to the CSCF controller 272via the PCRF controller.

After sending the measurement report at S232, the UE 210 may prepare toterminate the first call setup process and to initiate the second callsetup process. In one example, the UE 210 may wait for a terminationmessage from the CSCF controller 272 (S252). The termination message maybe an SIP 500 Server Internal Error response or an SIP 503 ServiceUnavailable response without requesting the UE 110 to make any retryattempts. After the UE 210 receives the termination message, at S256 theUE 210 may send to the CSCF controller 272 an SIP ACK Request thatacknowledges the receipt of the termination message.

In some examples, if the timeout timer is used, the UE 210 may wait forthe timeout timer reaches the predetermined value or wait for theearlier one of receiving the termination message from the CSCFcontroller 272 or the timeout timer reaching the predetermined value.When the timeout timer reaches the predetermined value at S254, at S256the UE 210 may send to the CSCF controller 272 an SIP CANCEL Requestthat notifies the cancellation of the first call setup process.

At S258, after the CSCF controller 272 receives the SIP ACK Request orthe SIP CANCEL Request from the UE 210, the CSCF controller 272 may sendan SIP CANCEL Request to SCC AS 274 (S258) to inform the cancellation ofsetting up the voice call using the EPC, and the SCC AS 274 may replywith an SIP 200 OK Response (S259) to acknowledge the cancellation ofsetting up the voice call using the EPC.

At S262, based on the timeout timer or the termination message from theCSCF 272, the UE 210 would be able to determine that the first callsetup process has been terminated and the second call setup process isto be initiated. At S264, the UE 210 sends via the eNB to the MME 222 aservice request to initiate the second call setup process for setting upthe voice call for the UE 210 using the CS core network. In someexamples, the service request may be an LTE Extended Service Request. AtS266, the MME 222, the eNB 228, and the MSC 232 work together to preparefor performing the second call setup process for setting up the voicecall for the UE 210. At S268, the MME 222 sends to the UE 210 aredirection message or a handover message with specific information withrespect to communicating with the MSC 232. In some examples, theredirection message or a handover message are LTE RRC connectionmessages.

As described with reference to FIG. 2, the UE 210 may be able toimplement the Circuit Switched Fallback (CSFB) functionality whenestablishing an outgoing voice call based on the signaling even when theservice network does not support the SRVCC feature.

FIG. 3 shows an exemplary signaling diagram of setting up an incomingcall for a user equipment (UE) 310 in a communication system, such asthe UE 110 in the communication system 100 in FIG. 1, according to anembodiment of the disclosure. FIG. 3 shows a signaling sequence amongvarious components, including the UE 310, eNB 328 of an E-UTRAN, MME 322of an EPC, CSCF controller 372 and SCC AS 374 of an IMS, and MSC 332 ofa CS Core network, which may correspond to the UE 110, eNB 128, MME 122,CSCF controller 172, SCC AS 174, and MSC 132 in FIG. 1, respectively.FIG. 3 only highlights example components and messages for illustratingthe disclosed embodiments. It is understood that additional messages,requests, and responses may be exchanged among the components depictedin FIG. 3, and additional components of the communication network mayalso be used for performing the signaling sequence depicted in FIG. 3.

At S310, the eNB 328 sends to the UE 310 a measurement configurationmessage that specifies a set of measurement events corresponding to poorsignal quality between the UE 310 and the packet-switched network,particularly between the UE 310 and the eNB 328 that connects the UE 310with the EPC. The set of measurement events may include the LTE A1, B1,and/or B2 measurement events. Also, the measurement configurationmessage may be implemented using an LTE RRC connection reconfigurationmessage.

At S322, the SCC AS 374 sends a request for initiating a voice call tothe CSCF controller 372. At S324, the CSCF controller 372 forwards therequest for initiating the voice call to the UE 310. The request forinitiating the voice call may be an SIP INVITE Request. At S326, the UE310 sends to the CSCF controller 372 a response indicating that the callsetup process is in progress, such as using an SIP 183 Session inProgress Response. At S328, the CSCF controller 372 may pass theresponse indicating that the call setup process is in progress to theSCC AS 374.

Although S310 as depicted in FIG. 3 is performed prior to S324, in someexamples, S310 may be performed after S324 or after S326.

At S332, when the UE 310 determines that one of the measurement eventsas specified in the measurement configuration message occurs, the UE 310sends a measurement report to the eNB 328. At S342, the CSCF controller372 may send a request to create a bearer for the voice call in a mannersimilar to S242 in FIG. 2. At S344, in response to the request to createa bearer, the eNB 328 determines whether to abort the voice call basedon the measurement report from the UE 310, the status of the call setupprocess, or whether the service network support the SRVCC feature, orthe like. When the eNB 328 determines to terminate the call setupprocess for setting up the voice call using the EPC and to initiateanother call setup process for setting up the voice call using the CSCore network, at S346 the eNB 328 informs the CSCF controller 372 thedecision in a response to the request to create a bearer in a mannersimilar to S246 in FIG. 2.

At S352, after receiving the response to the request to create a bearer,the CSCF controller 372 sends a cancellation message to the UE 310 tocancel the first call setup process. The cancellation message may be anSIP CANCEL Request. At S354, the UE 310 may send to the CSCF controller372 an SIP 200 OK Response that indicates the acknowledgement of thecancellation message. At S356, the CSCF controller 372 may also send tothe SCC AS 374 a failure response indicating that the incoming voicecall will not be setup using the EPC. In some examples, the failureresponse may be one of the SIP four hundred series Client FailureResponse. At S358, upon receiving the failure response, the SCC AS 374may send the CSCF controller 372 an SIP ACK Request that acknowledgesthe cancellation of the first call setup process.

At S362, the SCC AS 374 may further send to the CSCF controller 372another request for initiating a voice call using the MSC 332 of the CSCore network, and the CSCF controller 372 may forward the request to theMSC 332. At S364, the MSC 332 sends a paging message to the MME 322 thatindicates that the voice call will be setup using the MSC 332. At S366,the MME 322 sends to the UE 310 a service notification message thatindicates initiation of the second call setup process for setting up thevoice call using the MSC 332.

At S372, in response to the service notification message, the UE 310would be able to determine that the first call setup process has beenterminated and the second call setup process is to be initiated. AtS374, the UE 310 sends via the eNB to the MME 372 a service request toinitiate the second call setup process for setting up the voice call forthe UE 310 using the CS core network. In some examples, the servicerequest may be an LTE Extended Service Request. At S376, the MME 322,the eNB 328, and the MSC 332 work together to prepare for performing thesecond call setup process for setting up the voice call for the UE 310.At S378, the MME 322 sends to the UE 310 a redirection message or ahandover message with specific information with respect to communicatingwith the MSC 332. In some examples, the redirection message or ahandover message are LTE RRC connection messages.

As described with reference to FIG. 3, the UE 310 may be able toimplement the Circuit Switched Fallback (CSFB) functionality whenestablishing an incoming voice call based on the signaling even when theservice network does not support the SRVCC feature.

FIG. 4 shows a flow chart outlining an exemplary process 400 forchanging from a first call setup process to a second call setup processin order to setup a voice call for a user equipment, such as the UE 110in FIG. 1, according to an embodiment of the disclosure. It isunderstood that additional operations may be performed before, during,and/or after the process 400 depicted in FIG. 4. The process 400 startsat S401 and proceeds to S410.

At S410, a measurement configuration message is received by a UE. Themeasurement configuration message specifies a set of measurement eventscorresponding to poor signal quality between the UE and apacket-switched network, and particularly between the US and an eNB thatconnects the UE to the packet-switched network. In some examples, S410corresponds to S210 in FIG. 2 or S310 in FIG. 3.

At S420, the first call setup process for setting up the voice call forthe UE using the packet-switched network is performed. In some examples,S410 corresponds to S222-S228 and S242-S246 in FIG. 2 or S322-S328 andS342-S344 in FIG. 3.

At S430, it is determined whether the first call setup process is stillongoing. If the first call setup process is still ongoing, the processproceeds to S440. If the first call setup process is completed oraborted entirely, the process moves to S499 and terminates.

At S440, it is determined whether one of the measurement eventsspecified in the measurement configuration message has occurred. If oneof the measurement events specified in the measurement configurationmessage occurs, the process proceeds to S450; otherwise, the processproceeds to S430 to monitor the first call setup process as well as S440to monitor the measurement events.

At S450, a measurement report indicating that one of the measurementevents specified in the measurement configuration message has occurredis sent. In some examples, S450 corresponds to S232 in FIG. 2 or S332 inFIG. 3.

At S460, a timeout timer is setup. In some examples, S460 can beoptional and may correspond to S234 in FIG. 2.

At S470, it is determined whether a cancellation event occurs. If it isdetermined that a cancellation event occurs, the process proceeds toS480. If it is determined that a cancellation event has not occurred,the process stays at S470. In some examples, the cancellation event maybe receiving a termination message from the service network, such asS252 in FIG. 2. In some examples, the cancellation event may be thetimeout timer setup at S460 reaches a predetermined value, such as S254in FIG. 2. In some examples, the cancellation event may be receiving acancellation message followed by a service notification message from theservice network, such as S352 and S366 in FIG. 3.

At S480, a second call setup process for setting up the voice call forthe UE using a circuit-switched network is performed. In some examples,S480 corresponds to S264-S268 in FIG. 2 or S374-S378 in FIG. 3.

After S480 or S430, the process 400 proceeds to S499 and terminates.

While aspects of the present disclosure have been described inconjunction with the specific embodiments thereof that are proposed asexamples, alternatives, modifications, and variations to the examplesmay be made. Accordingly, embodiments as set forth herein are intendedto be illustrative and not limiting. There are changes that may be madewithout departing from the scope of the claims set forth below.

What is claimed is:
 1. A method for setting up a call for a userequipment, comprising: receiving, by the user equipment, a measurementconfiguration message that specifies a set of measurement eventscorresponding to poor signal quality between the user equipment and apacket-switched network; initiating, by the user equipment, a first callsetup process for setting up the call using the packet-switched network;sending, by the user equipment, a measurement report when one of the setof measurement events occurs while performing the first call setupprocess; receiving a termination message, the termination messageindicating termination of the first call setup process withoutrequesting the user equipment to perform retry attempts; and sending, bythe user equipment in response to receiving the termination message, aservice request to begin a second call setup process for setting up thecall for the user equipment using a circuit-switched network.
 2. Themethod according to claim 1, wherein the set of measurement eventscomprises at least one of: a first event where a signal strength from abase station that communicatively connects the user equipment and thepacket-switched network becomes less than a first threshold; a secondevent where a signal strength from a neighboring base station becomesbetter than a second threshold; and a third event that is a combinationof at least the first event and the second event.
 3. The methodaccording to claim 1, further comprising: receiving the terminationmessage after sending the measurement report.
 4. The method according toclaim 1, further comprising: starting a timeout timer when sending themeasurement report; and sending the service request after the timeouttimer reaches a predetermined value.
 5. The method according to claim 1,further comprising: receiving, by the user equipment from thepacket-switched network in response to the sent service request, aredirection message or a handover message specifying a controller of thecircuit-switched network.
 6. The method according to claim 1, furthercomprising: sending, by the user equipment in response to receiving thetermination message and before sending the service request, anacknowledgement message indicating the receipt of the terminationmessage.
 7. The method according to claim 1, further comprising:sending, by a base station that communicatively connects the userequipment and the packet-switched network, the measurement configurationmessage to the user equipment; receiving, by the base station, themeasurement report from the user equipment; and determining whether toterminate the first call setup process and to begin the second callsetup process based on at least the measurement report from the userequipment and call status of the user equipment.
 8. The method accordingto claim 7, further comprising: receiving, by the base station, a createbearer request from an Internet Protocol Multimedia Subsystem (IMS); andsending, by the base station to the IMS in response to the create bearerrequest, a create bearer response that indicates a determination resultof whether to terminate the first call setup process and to begin thesecond call setup process.
 9. A user equipment, comprising: atransceiver configured to communicate with a packet-switched network anda circuit-switched network; and a controller configured to: receive,through the transceiver, a measurement configuration message thatspecifies a set of measurement events corresponding to poor signalquality between the user equipment and the packet-switched network;initiate a first call setup process for setting up a call for the userequipment using the packet-switched network; send, through thetransceiver, a measurement report when one of the set of measurementevents occurs while performing the first call setup process; receive,through the transceiver, a termination message, the termination messageindicating termination of the first call setup process withoutrequesting the user equipment to perform retry attempts; and send,through the transceiver in response to receiving the terminationmessage, a service request to begin a second call setup process forsetting up the call for the user equipment using the circuit-switchednetwork.
 10. The user equipment according to claim 9, wherein the set ofmeasurement events comprises at least one of: a first event where asignal strength from a base station that communicatively connects theuser equipment and the packet-switched network becomes less than a firstthreshold; a second event where a signal strength from a neighboringbase station becomes better than a second threshold; and a third eventthat is a combination of at least the first event and the second event.11. The user equipment according to claim 9, wherein the controller isfurther configured to: receive the termination message after sending themeasurement report.
 12. The user equipment according to claim 9, whereinthe controller is further configured to: start a timeout timer whensending the measurement report; and send the service request after thetimeout timer reaches a predetermined value.
 13. The user equipmentaccording to claim 9, wherein the controller is further configured to:receive, from the packet-switched network in response to the sentservice request, a redirection message or a handover message specifyinga controller of the circuit-switched network.
 14. The user equipmentaccording to claim 9, wherein the controller is further configured to:send, in response to receiving the termination message and beforesending the service request, an acknowledgement message indicating thereceipt of the termination message.
 15. A communication system,comprising: a service network; and a user equipment configured tocommunicate with the service network, wherein the service network isconfigured to send a measurement configuration message that specifies aset of measurement events corresponding to poor signal quality betweenthe user equipment and a packet-switched network of the service network;the user equipment is configured to: receive the measurementconfiguration message; initiate a first call setup process for settingup a call for the user equipment using the packet-switched network senda measurement report when one of the set of measurement events occurswhile performing the first call set-up process; receive a terminationmessage, the termination message indicating termination of the firstcall setup process without requesting the user equipment to performretry attempts; and send, in response to receiving the terminationmessage, a service request to begin a second call setup process forsetting up the call for the user equipment using a circuit-switchednetwork after terminating the first call setup process.
 16. Thecommunication system according to claim 15, wherein the set ofmeasurement events comprises at least one of: a first event where asignal strength from a base station that communicatively connects theuser equipment and the packet-switched network becomes less than a firstthreshold; a second event where a signal strength from a neighboringbase station becomes better than a second threshold; and a third eventthat is a combination of at least the first event and the second event.17. The communication system according to claim 15, wherein the userequipment is further configured to: receive the termination messageafter sending the measurement report, and the service network is furtherconfigured to: receive the measurement report from the user equipment;determining whether to terminate the first call setup process and tobegin the second call setup process based on at least the measurementreport from the user equipment and call status of the user equipment;and send the termination message indicating termination of the firstcall setup process to the user equipment when the first call setupprocess is determined to be terminated.
 18. The communication systemaccording to claim 15, wherein the user equipment is further configuredto: start a timeout timer when sending the measurement report; and sendthe service request after the timeout timer reaches a predeterminedvalue.
 19. The communication system according to claim 15, wherein theservice network is further configured to: send, in response to theservice request from the user equipment, a redirection message or ahandover message specifying a controller of the circuit-switched networkto the user equipment.
 20. The communication system according to claim15, wherein the service network comprises: an Internet ProtocolMultimedia Subsystem (IMS); and a base station that is configured toreceive a create bearer request from the IMS, and send a create bearerresponse that indicates a determination result of whether to terminatethe first call setup process and to begin the second call setup processto the IMS in response to the create bearer request.